The following is a summary of “Vaccine Effectiveness Against Influenza-Associated Urgent Care, Emergency Department, and Hospital Encounters During the 2021–2022 Season, VISION Network,” published in the July 2023 issue of Infectious Diseases by Tenforde, et al.

For a study, researchers sought to assess the vaccine effectiveness (VE) against influenza-associated emergency department/urgent care (ED/UC) visits and hospitalizations during the 2021–2022 influenza season, which was predominantly caused by influenza A(H3N2) 3C.2a1b 2a.2 subclade.

A test-negative case-control analysis was conducted among adults aged ≥18 years at three sites within the VISION Network. The study included ED/UC visits and hospitalizations with at least one acute respiratory illness (ARI) discharge diagnosis code and molecular testing for influenza. VE was calculated by comparing the odds of influenza vaccination at least 14 days before the encounter date between influenza-positive cases (type A) and influenza-negative and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)–negative controls. The analysis involved the application of inverse probability-to-be-vaccinated weights and adjustment for confounders.

A total of 86,732 ED/UC ARI-associated encounters (7,696 [9%] cases) and 16,805 hospitalized ARI-associated encounters (649 [4%] cases) were included in the study. The VE against influenza-associated ED/UC encounters was 25% (95% confidence interval [CI], 20%–29%), and the VE against influenza-associated hospitalizations was 25% (95% CI, 11%–37%). However, VE against ED/UC encounters was lower in adults aged ≥65 years (7%; 95% CI, −5% to 17%) or with immunocompromising conditions (4%; 95% CI, −45% to 36%).

During the influenza A(H3N2)-predominant season, the study observed a modest VE against influenza-associated ED/UC visits and hospitalizations. The findings highlighted the need for improved vaccines, particularly for A(H3N2) viruses that historically have been associated with lower VE.

Source: academic.oup.com/jid/article/228/2/185/6997868